Onsite Wastewater Treatment Systems
Municipal Officials Conference:
Managing Onsite Wastewater Treatment Systems
to Protect Long Island’s Waters
March 25, 2014
George Loomis
New England Onsite Wastewater Training Program @ URI
• We are a USDA, state and training class fee funded program
• Outreach through URI Cooperative Extension
• Coverage area: Regions 1&2 – New England, NY, NJ, PR &
USVI
• Provide third party, non-biased technical assistance
• Clientele includes federal and state regulatory agencies,
communities, NGOs, wastewater professionals, homeowners
• Conduct approx. 50 classes a year reaching over 1,800
wastewater practitioners and decision makers
• We perform onsite wastewater research
• Work closely with local and state regulatory programs
NEOWTC @ URI
Long Island and Block Island Sound
What we will cover –
1) Conventional OWTS basics
2) Cesspools
3) Contaminant treatment potential
4) System management - inspection and tank
pumping
5) Intro - Advanced treatment technologies (more
in afternoon session talk)
1) Conventional septic system has
3 main components
Septic tank Soil absorption area
Source: URI Cooperative Extension, New England Onsite Wastewater Training Center
D-Box
Conventional Septic Tank
Inlet
sludge
scum
As scum and sludge layers build and come closer
together, the retention time becomes less and
solids removal efficiency drops, as well as BOD and
FOG removal
Conventional D-Box
Operates on trickle flow
to the lowest pipe invert
D-Box leveling
devices readjust
outlet pipe inverts.
Manufacturers make these for
various pipe sizes.
Separation distance
Defined as: The distance between the base
of a drainfield and the elevation of
the seasonal high water table (or a
restrictive layer)
This varies with jurisdiction. Nassau Co. has a minimum separation to SHWT of 24”
Suffolk Co. has a minimum separation to SHWT of 36”
Drainfield options
Drainfield sizing criteria
• Depends on the soil type
• Number of bedrooms
• The design of a soil treatment area also
depends on the type of system.
• Leaching pools are designed differently
than pipe on stone (tile drainfields).
Min. separation distance to water
table = 3 or 4 feet (Rhode Island)
• In 2008, galleys prohibited in RI for new construction
• Block Island will phase out existing ones
• Produces a deep
installation base
(8 ft.)
• Poor oxygen
diffusion
• Poor aerobic
treatment
potential
2’
8’ 2’
10”-14”
3.5’+/-
Alternative system (shallowest chamber type for shallow SHWT)
Leaching pools
6’
Typical 4 bedroom leaching pool design
(for SHWT 9’ or greater)
8’
Typical 4 bedroom leaching pool design
(for SHWT 11’ or greater)
14’
Typical 4 bedroom leaching pool design
(for SHWT 17’ or greater)
25’ max
A very deep installation
Concentrated footprint
Small infiltrative surface
• NO septic tank
• Substandard system
• Antiquated and inadequate
• Often violates vertical separation distance regulations
• In coastal areas - may be tidally connected
• Prioritize replacement with approved system
2) Cesspools
Source: URI Cooperative Extension, New England Onsite Wastewater Training Center
2) Cesspools defined -
Dry-fit, or minimally
mortared: Concrete
block, brick, fieldstone
Into which flows
sanitary sewage from
a structure
Impractical - solids
storage and liquid
infiltration
Treatment and safety
issues
3) Pollutants common in septic
tank effluent
• TSS, BOD5
• Nutrients - nitrogen, phosphorus
• Volatile organic chemicals (VOCs)
• Pathogenic organisms
- Helminths (septic worms)
- Protozoa
- Bacteria
- Viruses
Vadose zone wastewater treatment
Controlling factors –
• Environmental
Temp., moisture,
oxygen levels
• Wastewater char.
Loading rates,
strength, types
of pollutants
• Soil properties
Physical, chemical,
biological
• Retention time
Unsaturated soil
Water table
Saturated soil
Biomat
Soil-based wastewater treatment
The Goal :
• Unsaturated conditions
• Thin film flow of wastewater
around soil particles
• Pore space in between
particles and/or soil peds
(structural units of soil)
• Gases and air move
in/out
When organic inputs exceed removals and all
soil pore spaces are clogged, then hydraulic
failure occurs.
Failure defined (usually in regs):
Surfacing wastewater = off site movement of
contaminants, loss of treatment, water quality
impairment, and environmental and public
health risks
Source: URI Cooperative Extension, New England Onsite Wastewater Training Center
Biochemical reactivity in soils
• 99% of soil bioreactivity is within 10 – 20 inches of soil surface
Sources:
“Introduction to Soil Microbiology”, Second Edition – Martin Alexander - John Wiley & Sons,1977.
"Soil Microbiology" Selman Waksman - John Wiley & Sons, 1952.
MOST OWTS regs promote deep drainfield placement, well below this reactive zone
Summary - Nitrogen removal in
conventional septic systems
• Less than 15 percent removal in septic tank
• Septic tank effluent composed of organic-N
and ammonium-N
• Limited ammonium adsorption by soil below
drainfield
• Ammonium conversion to nitrate-N
• Nitrate-N very mobile and conservative
• 10 ppm EPA nitrate-N drinking water standard
Summary - Phosphorus (P) removal in
conventional septic systems
• Phosphorus adsorbed to iron, aluminum,
manganese, calcium, and magnesium in
soils
• P removal depends on soil surface area
• Sands have far less surface area than finer
soil particles
• P saturation can and does occur
• Wet soils conditions result in iron removal, so less P removal potential
Summary - Wastewater
microorganism movement
Organism Approx. Size Mobility
Potential
Helminths
Protozoa
Bacteria
Viruses
sand
c. silt
f. silt - c. clay
v.f. clay
low
high
Enhanced removals with aerobic soils and long retention times
Summary –
Emerging contaminants of concern
• Pharmaceuticals
• Antimicrobials
• Endocrine disrupters
• Personal care products (PCPs)
Removals based upon complex biochemistry –
and they are compound and site specific
Aerobic soil conditions and long retention times
are key treatment factors
Life cycle of an unmanaged
conventional septic system
---------- Years----------
T0 Tff Thf siting
design
permitting
installation
home first
occupied
system
hydraulically
fails
// (first flush)
USE
T = time
4) Management
The onsite system
O&M image crisis
Anything beyond
nothing seems like
too much !
Onsite wastewater industry challenge
• Managed centralized treatment plants
• Unmanaged conventional systems
• Managed advanced treatment onsite
systems
Conventional system inspections and tank pumping
Identifies problems Creates an inventory
Protects –
•Owner investment
•Public health
•Water quality
•Resources
•Property values
Managed systems last longer than neglected ones
Costs - $250 (pumping) and $50 to150 (inspection)
Frequency – every 3 to 5 years
Onsite Wastewater Treatment System
Inspector Training Class
Dates & Times:
April 22 – 23, 2014 (2-day class) 8:00 am – 5:30 pm (registration at 7:30 am)
or
April 24 – 25, 2014 (2-day class) 8:00 am – 5:30 pm (registration at 7:30 am)
Location:
Oyster Bay Community Center, Church Street, Oyster Bay, NY 11771
Cost: FREE (normal cost $450)
Class size is limited to 25 people, so please register early to assure a seat.
5) Alternative technology
treatment train
1. Primary treatment zone
2. Alternative technology
Secondary treatment 3. Drainfield - Dispersal and advanced secondary / tertiary treatment 4. Controls - timers
• Totally unsewered watersheds
• 30 - 50 % of systems are cesspools
• Very permeable unconfined aquifers
• Groundwater contamination risk
• 8 houses / acre on shallow wells
• Surface water eutrophication risk
• Shellfish closures
Water quality standards for coastal pond systems
• 0.3 - 0.5 mg/l TN and 14 counts / 100 ml F. coliform
Typical application for I&A technologies
Rhode Island southern coast
Advanced treatment technologies approved in RI
ca.1996
• RUCK
• ATUs
• Single pass sand filters
• Recirc. sand filters
• Early textile filters
• Foam biofilters
• Shallow narrow pres. drainfields
• Bottomless sand filters - early
• Modular peat filters
• Textile filters
• Fixed activated sludge systems
• Bottomless sand filters – current
• Denite upflow filters
• Trickling filters
• UV disinfection
• Soil treatment area renovation technologies ca.2014
ca.1983
N removal systems
Bottomless sand filter
Thanks for your attention!
George Loomis
401. 874. 4558
http://www.uri.edu/ce/Cwq/OWT/index.htm